1. Field of the Invention
The invention relates to aspiration of blood for autologous blood transfusion and more particularly to structure and method for metering anticoagulant to the aspirated blood.
2. The Prior Art
Intraoperative autotransfusion is increasingly recognized as providing an effective means of returning blood lossed at the operating site directly to the patient without the recognized complications and disadvantages of stored bank blood. It is recognized, however, that widespread autotransfusion has not been uniformly adopted heretofore in large part because of the inability to meter the appropriate amount of anticoagulant to the blood in the course of aspiration.
Historically, two primary techniques were used to control the coagulation of autologous blood. First, anticoagulant such as acid citrate or heparin have been introduced by "in line" drip directly into a collection reservoir. This method requires constant monitoring to assure proper anticoagulation and does not prevent clot formation in the vacuum line between the suction tip and the collection reservoir.
A second technique is referred to as systemic heparinization. According to this technique, anticoagulant is injected intravenously in sufficient amounts that all of the patient's blood is affected by the anticoagulant. While this method has proved satisfactory for selected kinds of peripheral vascular surgery, it has not been accepted in those patients in whom a significant amount of soft tissue dissection is anticipated or in patients suffering from multiple trauma. Further, systemic heparinization has made post-operative hemostasis much more difficult.
Most recently, efforts have been made to deliver anticoagulant to blood as the blood passes through a venturi in the handle of an aspiration wand. See, for example, U.S. Pat. No. 3,807,401 and the American Journal of Surgery, Volume 123, March 1972, page 257 et. seq.
The trauma involved in passing whole blood through a venturi has proved to be undesirably hemolytic. Furthermore, the complicated construction of such devices generally makes them too expensive to be disposable. Finally, special exterior valving structure is required to prevent retrograde flow of the anticoagulant from the suction wand at the conclusion of each aspiration.
It would therefore be a valuable contribution to the art to provide an improved aspiration wand with an anticoagulant metering device which forms an effective positive control on the volume of anticoagulant metered to aspirated blood in a facile and inexpensive manner.